feat: TMDB year fallback + PUID/PGID support

- tmdb.py: store release_date year in cache, expose as tmdb_year
- main.py + app.js: use tmdb_year when subtitle has no year
- Dockerfile: add gosu + abc user for PUID/PGID runtime privilege drop
- entrypoint.sh: new entrypoint handling PUID/PGID ownership of /app/data

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

README.md

@@ -101,6 +101,8 @@ TMDB_API_KEY=xxx docker compose up -d
 | `TMDB_API_KEY` | — | Clé API TMDB (obligatoire pour posters/backdrops) |
 | `TZ` | `UTC` | Fuseau horaire |
 | `AUTO_DL_INTERVAL` | `3600` | Intervalle (secondes) entre deux checks auto-DL |
+| `PUID` | `0` | UID Unix du propriétaire des fichiers (Unraid : `99`) |
+| `PGID` | `0` | GID Unix du propriétaire des fichiers (Unraid : `100`) |
 
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